Donna, you don't say what climate zone you are in, or which crape myrtle...there are some newer varieties that are more tolerant of cold, but depending on variety, crape myrtles can be grown from USDA hardiness zones 6 to 10. In zone 6, even the most cold-hardy varieties will probably be killed to the ground each winter and will be useful only as a shrubby, flowering perennial. I have to add too, that I have 'Zuni' in my own Z8 coastal garden in my hottest possible position with my light colored house to reflect heat - in 10 years time it's an interesting small tree with bronzy foliage and great peeling bark but it's never ever bloomed. Not enough summer heat.

Very fresh seed that hasn't been stored or dried will often germinate, very lightly covered as some light may be beneficial to germination, 70-75F, without the cold period preceding sowing.

If the seed has dried, as George notes in the other crape post: stratify 4 weeks at 40F, lightly cover the seed, soil temp 70-75F & takes 15-20 days to germinate & 15 weeks to reach large enough to set out - so you'll have to calculte your own average last frost date and count backwards.

Depending on what kind of setup you have for growing seedlings, crepe myrtle seeds can be started in mid to late winter in order to get decent-sized plants by the time they're set out when warm weather arrives in spring. If you have adequate light, the young plants will remain healthy until they're transitioned into the garden.

There are crepe myrtles (especially some dwarf varieties) that will be hardy into USDA zone 5 as returning perennials, blooming nicely if (as the previous poster noted) they have adequate summer heat, and if there's full sun. I grow several varieties of crepes here on the northern fringe of zone 6 and some types will flower heavily for months. In a mild winter most to all of the wood of the hardier types will survive, meaning earlier blooming.

Your chances of getting a tree form crepe in eastern Canada are not good, but depending on where you're located and whether a sheltered spot is available, you can still have flowering crepes as perennials/shrubs.